In an auction, how might magic item collectors in other lands bid remotely?

There is no magic item retail in my world. Instead, common to rare items are often sold at special auctions curated by the Order of the Sphinx, a wizard guild. Typically, the items for sale at these auctions are old heirlooms from bankrupted lords, the spoils of war sold by the state for revenue, and the occasional relic unearthed by a lucky farmer tilling their field.

My campaign is set in a semi-backwater region that is not home to many magic users or magic items; it would not be uncommon for the monthly magic item auction to have nothing to bid on at all. But when a treasure does turn up, wealthy collectors and powerful wizards from far off lands bid by proxy.

I’m thinking a wealthy collector might give discretion to well-paid hirelings in major cities to seek out certain types of items, within a price range. Powerful mages, however, would likely use magic to participate remotely in these auctions. What type of magic could they use?

I am looking for RAW spells and magic items that could facilitate remote bidding. Two examples that come to mind are astral projection and sending stones, but I’d love to know other options too, for the sake of variety and flavor.

At some point I might homebrew an option, but I’d like to establish what the RAW baseline is first to avoid redundancy.

Bidders might be as far away as 5000 miles from the actual auction location.

Please consider the cost of your suggested remote bidding strategies. The items in question (again, only common to rare) are valued within the same ranges indicated on page 135 of the Dungeon Master’s Guide, so between 50gp and 5,000gp.